Figure 9.

Working model for the negative regulation of plant systemic defense through MeSA glucosylation. When plants are infected by some pathogens, MeSA levels rise rapidly in the primary infected plant tissues. UGT71C3 is up-regulated due to the induction of pathogens and MeSA. MeSA glucosylation is thus accelerated, resulting in less MeSA being transported to the uninoculated systemic tissues. In the systemic tissues, MeSA is further glucosylated by UGT71C3, resulting in further reduced MeSA levels and thus a reduced level of SA, which is converted from MeSA. Thereby, the expression of pathogen-related proteins decreases and defense responses are attenuated. The downward arrows mean the decrease of MeSA and SA levels or down-regulation of PR genes. AtMES, Arabidopsis methylesterases; BSMT1, SA methyl transferase 1.